As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature processed) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is formed by folding and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a layer of fibrous material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of oxygen-barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
Such packages are normally made on fully automatic packaging machines, on which a continuous tube is formed from the packaging material supplied in strip form; the strip of packaging material is sterilized on the packaging machine itself, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, after sterilization, is removed, e.g. vaporized by heating, from the surfaces of the packaging material; and the strip of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut at equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the resulting packages are filled with the food product and sealed. One example of such a package is the so-called "gable-top" package commonly known by the trade name Tetra Rex (registered trademark).
To open such packages, various solutions have been proposed, one of which, described in U.S. Pat. Nos. 4,655,387 and 4,410,128, consists in forming, at the corner of a flap on the package, a preferential tear line defined by a succession of perforations extending through the outer layers of the packaging material down to the layer of barrier material; and the package is opened by lifting the flap and cutting or tearing along the perforations. Packages of this type, however, cannot, obviously, be closed once opened, and must therefore be handled with care to prevent spillage of the remaining food product inside the package.
By way of a solution to the problem, packages of the type described above have been provided with closable opening devices, which substantially comprise a frame defining an opening and fitted over a hole or a pierceable or tear-off portion in a wall of the package; and a cap hinged to the frame. The cap is normally molded integrally with the frame, and is initially sealed to the frame, along a peripheral edge surrounding the opening, by a thin breakable annular connecting portion. Once unsealed, the cap is movable between a closed position cooperating in fluidtight manner with the frame, and an open position. Alternatively, threaded caps are also used, which are separate from and initially screwed to the frame.
One problem posed by such opening devices is ensuring practically no effort is required to detach the cap from the frame when unsealing the package. For which reason, the opening devices are made of low-tear-strength plastic material, normally polyethylene.
Since polyethylene, however, fails to act as an effective oxygen barrier, the side of the packaging material eventually defining the inside of the package must be fitted over the hole with an additional patch member defined by a small sheet of heat-seal plastic material; and the opposite side of the packaging material must be fitted with an oxygen-barrier member, e.g. a pull-off tongue, heat sealed to the patch member and comprising a layer of aluminium.
Providing the packages with barrier and patch members calls for additional processing of the packaging material, before this is sterilized and folded and sealed into a vertical tube, thus increasing the production time and cost of the packages.
Moreover, after unsealing the cap, the user must also remove the barrier member to open the package.
Closable opening devices have therefore been devised to enable the package to be opened in one operation, while at the same time ensuring an effective oxygen barrier.
According to the solution described in International Patent Application WO 95/05996, such opening devices substantially comprise a frame having a cylindrical collar defining a pour opening and fitted about a pierceable portion of the package; a removable cap which screws onto the outside of the frame collar to close the opening; and a substantially tubular cutting member screwed inside the frame collar and having an end edge with a number of substantially triangular end teeth, which cooperate with and partly detach the pierceable portion of the package from the relative wall, i.e. with the exception of a small-angle portion.
The cutting member is activated by the cap by means of one-way ratchet-type transmission means--operated during disengagement of the cap from the collar--and is movable in a spiral with respect to the frame from a raised rest position, in which the end teeth face the pierceable portion, into successive lowered cutting positions in which the end teeth interact with the pierceable portion.
One drawback of opening devices of the above type is that the cut part of the pierceable portion tends, in use, to at least partly clog the opening of the cutting member and, hence, the pour opening, thus obstructing outflow of the product from the package.
Also, for functional reasons, the cutting member is normally made of structurally more rigid material (e.g. polypropylene) than the frame and cap (normally made of polyethylene), with the result that the end teeth of the cutting member are highly fragile and may undergo severe damage when transporting or handling the packages, even to the extent of breaking when unsealing the package and possibly being dispersed in the food product itself.